The present invention relates to a substrate transport unit for transporting a work piece such as a semiconductor wafer, a substrate for a photomask or a glass substrate for a liquid crystal display by using a double armed robotic hand.
Conventionally, a substrate transport unit is known wherein two robotic hands are provided on a base so that a replacement operation of work pieces, such as semiconductor wafers, substrates for photomasks or glass substrates for liquid crystal displays is possible in a short period of time (see, for example, Japanese unexamined patent publication No.8-274140). In this type of substrate transport unit, two base arms are formed in positions symmetric to each other, with one on the left and the other on the right, and are offset from the center of the robot so that the work pieces, which are transport objects, are shifted through the operation of these arms.
At this time, the tip parts of the right and left arms are offset to the right and left having a plane including the center line of the substrate transport unit as a symmetrical plane and since the minimum rotational radius of the robot, including a work piece to be transported, becomes significantly large in the case that end effectors are directly attached to tip parts of these arms, U-shaped bars that are directed to the symmetrical plane from the tip parts of the right and left hands of the substrate transport unit are provided and end effectors are attached to these U-shaped bars so that a structure is provided wherein a work piece can be placed. In addition, these U-shaped bars vary in dimension according to the size of a work piece to be transported in order to prevent the work pieces placed on the respective end effectors from interfering with each other at the time of arm extension or contraction.
In order to increase productivity, a clean transport unit that is compact and of which the transport time is short is in demand wherein as great a distance as possible is maintained between the part to be processed, such as a substrate, and a robot, which is a transport part, and wherein the unit is designed so as to save space. At the same time, an increase in reproducibility of repetitive transport and in mechanical rigidity at the time of operation is required for advanced microscopic processing and, therefore, these problems have become the focus of development.
In the above described conventional substrate transport unit, however, as shown in FIGS. 3(b) and 4, base arms B1 and B2 are formed in positions that are offset from the center of the unit and are symmetrical on the right and left. Therefore, the end effectors E1 and E2 above the base arms that extend to the right and left have, in some cases, different assembly errors on the right and left sides at the stage of manufacture and, therefore, the level standard of the end effectors E1 and E2 may differ. In addition, since the end effectors E1 and E2 are separated on the right and the left, a sidewise U-shaped bar B is provided in order to prevent interference between a work piece W, which is transported in an up and down direction, and an end effector. Therefore, such a U-shaped bar B lowers precision and rigidity.
The present invention is provided to solve these problems and an object thereof is to provide a double arm substrate transport unit that is a substrate transport unit for transporting a work piece, such as a semiconductor wafer, and wherein it becomes possible to eliminate a U-shaped bar by forming first and second forearms extending from the tip part of a base arm and, in addition, it becomes possible to reduce the number of parts and to reduce the total weight of the unit in comparison with a conventional substrate transport unit, wherein two base arms exist, one on the right side and the other on the left side.
In order to achieve the above object, the present invention provides a substrate transport unit for transporting a work piece, such as a semiconductor wafer, a substrate for photomask or a glass substrate for a liquid crystal display, by using a robotic hand that is formed of:
a base arm (20) that is supported by the base so as to rotate freely as shown in FIGS. 1, 2, and the like;
a forearm (A1) that is supported by the tip part of this base arm (20) so as to rotate freely;
an end effector (E1) that is supported by the tip part of this forearm (A1) so as to rotate freely and on which a work piece is placed;
a forearm (A2) that is supported by the tip part of the base arm (20) so as to rotate freely and that is attached above the forearm (A1) so as to overlap the forearm (A1); and
an end effector (E2) that is supported by the tip part of this forearm (A2) so as to rotate freely and on which a work piece is placed.
According to the present invention, the forearm (A1) and the forearm (A2) are formed above the base arm (20) and, therefore, the U-shaped bar (B), which is required in a conventional substrate transport unit shown in FIGS. 3(b) and 4, becomes unnecessary. Therefore, the mechanical precision of the forearm (A1) and of the forearm (A2) is primarily determined by the mechanical precision of the tip part of the base arm (20) so that the reproducibility, with respect to mechanical precision, of the forearm (A1) and the reproducibility of the forearm (A2) are of approximately the same values and it becomes possible to maintain the transport reproducibility of work pieces (W1) and (W2), which are placed on respective end effectors (E1) and (E2), at a high reproducibility.
In addition, as is seen by comparing FIG. 3(a) and FIG. 3(b), though the minimum rotational radius of the substrate transport unit of the present invention is R265 (mm), which is the same as of the conventional unit, the stretch stroke when the arm extends becomes st585 (mm), in comparison with st480 (mm) of the conventional unit, so that 20% of the stroke extension is achieved. Furthermore, though the forearms are formed to be symmetrical on the right and left side in the conventional unit so that the absolute volume occupied by the unit and the area as seen from above become large, all of the forearms and the base arm are put together on one side of the center line, as seen from above, of the unit of the present invention so that the freedom of the design layout becomes great of surrounding equipment when the unit of the present invention is utilized. Furthermore, the total number of components can be reduced so as to achieve a reduction in weight.
Furthermore, in the above structure according to the present invention, the forearm (A1) and the forearm (A2) have the same arm length, share a common rotational axis above the base arm (20) and are independently rotatable in planes of which the height positions are different from each other. Thereby, the arm becomes rotatable with a small radius so that a compact transport unit can be implemented.
In the above structure according to the present invention, three independent motors are provided in a box placed in the lower part of the unit that is formed of transmission means such that a motor (M1) rotates the base arm (20), a motor (M2) rotates the forearm (A2) and a motor (M3) rotates the forearm (A1). Thereby, three independent motors are driven in synchronization or independently so that it becomes possible to carry out the operation of which the movements are shown in operational diagrams (A) through (E) of FIG. 5, wherein the motor (M1) drives the base arm (20), the motor (M2) drives the forearm (A2) and the motor (M3) drives the forearm (A1) so as to have an operation of which the freedom is high due to the transmission method.
In the above structure according to the present invention, in response to one driving mode of the motors, the forearm (A1) moves backward or forward and the forearm (A2) carries out a circular movement having the rotational axis of the base arm (20) as the center. In response to another driving mode of the motors, the forearm (A2) may go backward or forward and the forearm (A1) may carry out a circular movement having the rotational axis of the base arm (20) as the center. Thereby, it becomes possible to move the end effector (E1) and the end effector (E2) backward or forward in a straight manner to or from the position where a work piece is given or received so that a replacement operation of work pieces becomes possible.
In the above structure according to the present invention, the robotic hand can, in response to a driving mode of the motors, rotate in an arbitrary rotational direction having the base arm rotational axis as the center while maintaining the angle formed by the base arm (20) and the forearm (A1) and the angle formed by the base arm (20) and the forearm (A2). Thereby, a rotational movement of the robotic hand becomes possible so that it becomes possible to freely arrange the position where a work piece is given or received relative to the substrate transport unit.
In the above structure according to the present invention, by making the motor (M1) and the motor (M2) or the motor (M3) rotate asynchronously, a work piece placed on the end effector (E1) or on the end effector (E2) may be moved within the targeted transport range by passing through an arbitrary track. For example, by rotating the motor (M2) or the motor (M3) while the motor (M1) is stopped, a work piece placed on the end effector (E1) or on the end effector (E2) is shifted backward or forward through a predetermined arc track. Thereby, in the case that there is an obstacle between the place where a work piece is given or received and the transport unit body, the arm is shifted so as to avoid the obstacle before the work piece placed on the end effector (E1) or on the end effector (E2) can be shifted to the place where the work piece is given or received.
In the above structure according to the present invention, the motor (M2) and the motor (M3) may be rotated synchronously in the same direction while the motor (M1) may be rotated asynchronously to, or in the direction opposite to, the rotational direction of the motor (M2) and the motor (M3) and, thereby, a work piece placed on the end effector (E1) and a work piece placed on the end effector (E2) can be simultaneously transported between the standby position and the position where a work piece is given or received. Thereby, it becomes possible to simultaneously transfer work pieces (W1) and (W2) by making the interval between the absorption surfaces of the respective end effectors (E1) and (E2) equal to the pitch between the slots of cassettes into which work pieces are loaded so that the transport throughput can be increased.
In the double arm substrate transport unit formed as described above according to the present invention, the motors may be provided along the rotational axes of the respective arms and end effectors so that the arms and the end effectors, respectively, are freely rotatable. Thereby, since it is possible to freely rotate each joint, it becomes possible to implement a greater variety of transport tracks.